This invention relates to the field of wired communication and control systems, in particular to such systems which provide for simultaneous distribution of power and message information along the network wires in a network having a plurality of sensors, actuators and processing elements.
Ethernet-based networks are popular as Local Area Networks (LANs) used for computer and communication networks, and are standardized under IEEE802. The network physical media are usually based on copper conductors, interconnecting between the various units comprising the network. Usually twisted-pair or coaxial cables are used. Terminals constituting Data Terminal Equipment (DTE) are connected to the network via xe2x80x98network adapterxe2x80x99 units that are tapped into the media. The adapters (also referred to as xe2x80x98nodes, network card etc.) handle the interface between the media comprising the bus and the payload units. In a LAN environment, the network adapters are usually housed within the DTE enclosure, and both the DTE and the adapter are locally powered by a power supply within the DTE enclosure. However, in some control networks, power is distributed centrally via the network so as supply power either to the network adapters only or to both the network adapters and the payloads.
FIG. 1 shows such a network 10 comprising a backbone or bus 11 having power and data lines 12 and 13, respectively. A dedicated power source 14 is connected across the power lines 12 whilst various adapters 15, 16 and 17 are connected across both the power and data lines 12 and 13 so as to receive power and allow for bi-directional communication with other adapters via the bus. The adapters 15, 16 and 17 can be standalone units (xe2x80x98hubxe2x80x99 units), or housed in the DTE enclosure, as is the case in network cards which are housed within a Personal Computer enclosure. The use of the dedicated power source 14 that provides power to all of the adapters in the network obviates the need to supply power locally to each of the adapters separately.
Payloads 18, 19 and 20 are connected to the adapters 15, 16 and 17 respectively. As seen, the payload 18 has both power and data connections to the adapter 18 so as to receive power therefrom and effect bidirectional data communication therewith. The payload 20 is connected directly to the power lines 12 so as to receive power directly therefrom, whilst the payload 19 is powered via a local power supply 21. It should be noted that in the following description and annexed figures, the terms xe2x80x9cpower sourcexe2x80x9d and xe2x80x9cpower supplyxe2x80x9d are used interchangeably.
U.S. Pat. No. 5,475,687 (Markkula et al.) is representative of a large number of patents describing networks employing the same xe2x80x98busxe2x80x99 network topology for control and automation. Specifically, nodes are used to interface between the network media and the sensors/actuators used as payloads. Similar to the LAN application, the nodes can be integrated into the payload or used as standalone units.
Although control networks can use the same powering scheme as described above, where each payload and its associated node are independently locally powered, other approaches are more popular in order to reduce wiring and powering complexity. The most popular powering method involves carrying the power in the network wires in addition to the data. This is usually performed using one of the following possibilities:
(a) Additional dedicated power wires are used along with the data wires, as shown in FIG. 1 and described in U.S. Pat. No. 5,469,150 (Sitte).
(b) Power and data are transmitted together over the same media, as described in U.S. Pat. Nos. 5,454,008 (Baumann et al.) and 5,148,144 (Sutterlin et al.) In this case, each node contains special circuitry in order to separate the data and power. In addition, means (shown as xe2x80x9cSource Couplerxe2x80x9d in FIG. 2) must be provided to interface the power supply to the bus in order that the low source impedance and power supply noise do not affect the dataxe2x80x94transmission in the network.
FIG. 2 shows schematically a network 25 employing so-called xe2x80x9cToken Ringxe2x80x9d topology, wherein a plurality of nodes is serially connected one to another. In addition, the network conforms to such an arrangement so as to send both power and data along the same wires. The network 25 comprises a bus shown generally as 26 fed by a power source 27 interfaced to the bus 26 by means of a source adapter 28. The source adapter 28 ensures that the low-source impedance and supply noise do not affect the data communication in the network. Network adapters or nodes 30, 31 and 32 are serially connected to the bus 26 via discrete bus sections 26a, 26b, 26c and 26d so as to receive combined power and data signals therefrom and feed data signals thereto. Payloads 33, 34 and 35 are connected to the adapters 30, 31 and 32 respectively. The payloads 33 and 35 have both power and data connections to the respective adapters 30 and 32 so as to receive power therefrom and effect bidirectional data communication therewith. In contrast thereto, the payload 34 is powered via a local power supply 36. In this case, each node contains special circuitry in order to separate the data and power.
Although the power carried in the bus 26 can be used for both the nodes and the payloads (as shown in payloads 33 and 35), this imposes a limit either on the power consumption of the payload or on the total length of the wires constituting the network. This limitation is overcome by the combined approach shown in FIGS. 1 and 2, wherein the nodes (usually low-power units) are powered from the network, while highly consumption payloads such as 19 and 34 are locally fed.
U.S. Pat. No. 5,095,417 (Hagiwara et al.) describes a control network employing Ring topology wherein nodes are connected in cascade in a manner similar to that shown in FIG. 2. The two end nodes are likewise cascaded so as to form a complete ring. Similar to the above discussion, separated or combined power/data lines can be used, and nodes/payloads can be powered locally or from the network.
In all types of buses described, regenerators are usually allowed. Regenerators (also referred to as repeaters, routers, bridges etc., according to their complexity and functionality) are used in order to extend the bus length limit. In addition, repeaters can also be used for connecting two distinct, physically separate networks performing different functions. The repeater is usually added as xe2x80x98cut and addxe2x80x99, in series with the existing lines. Similar to nodes, repeaters can be fed locally or from the network. The latter is preferred, since there is then no need to route additional wires to the repeater.
As demonstrated above, networks can be categorized as follows:
(a) Wiring topology. Either xe2x80x98busxe2x80x99 topology can be used, as demonstrated in FIG. 1, or xe2x80x98serially connectedxe2x80x99 wiring topology can be used (illustrated in FIG. 2). Mixed networks can also be implemented. For example, data lines can be serially connected in cascade while the power lines are connected in xe2x80x98busxe2x80x99 topology.
(b) Powering scheme. Three powering schemes can be employed. The first involves the case where the network adapters and the payloads are locally fed. This is usually the case in LAN systems, where line powering is not used. The second scheme involves the case where the nodes are fed from power carrying wires included in the network wiring, as shown in FIG. 1. The third option refers to the case where the payloads are also fed from the network, either by directly connecting to the network wiring (Payload 20 in FIG. 1) or fed via the network adapter (Payload 18 in FIG. 1). Mixtures of the above schemes can also be implemented, as described in FIGS. 1 and 2.
Known network configurations using line powering as described above with reference to FIGS. 1 and 2, employ a single power supply only, usually connected at an end of the line, although this is not mandatory. This approach suffers from the following problems:
(a) Range limitation. The DC resistance of the wires causes loss of power which is dependent upon the wire resistance (effected by diameter and resistivity) and its length. As such, the wires are subjected to a maximum length limitation. This can be overcome by raising the voltage used (similar to the way electrical supply utilities distribute electrical power). However this solution is problematic owing to safety issues, and is also more complicated and expensive owing to the need for wide-input range converter in the nodes.
(b) Source Reliability. In the case of power supply failure, the whole network crashes due to lack of power to the nodes.
(c) Redundancy. In the case of a failure in any of the nodes or in the wires (short or cut in any power-carrying wire), the part of the network beyond the failure point will not be powered, and will stop functioning. Furthermore, a short in the power lines may stall operation for the whole network.
(d) Lack of xe2x80x98Hot-swapxe2x80x99 capabilityxe2x80x94i.e. there is no capability to add, remove or change a power supply without any effect on the network operation. This is very problematic for maintenance, where it may be required to upgrade the network by adding a power supply, changing its power capacity etc.
The above-mentioned problems associated with the use of only a single power supply may be overcome by using multiple power supplies to power the network, employing similar techniques to those used to power a single load. FIG. 3 shows a known prior art system depicted generally as 40 conforming to this approach comprising a load 41 powered by multiple power supplies of which three are shown, enumerated 42, 43 and 44 coupled to the load 41 via respective supply adapters 45, 46 and 47. Such a configuration addresses three of the drawbacks associated with systems employing a single power supply only:
(a) Redundancy. In the case of failure in any of the power supply units, the remaining power supply units continue to feed the load. If any output on one power supply shorts or simply shuts down, the other remaining power supply units will take over and supply the full rated load.
(b) Source Reliability. Each power supply unit may feed portion of the required power. Consequently, each power supply unit may operate at less than rated capacity, resulting in higher reliability.
(c) Hot-swap capability. One or more power supply units can be added, removed or changed without any effect on the network operation.
Various types of stand-by are known. In xe2x80x98Hot Stand-byxe2x80x99 only one unit is active, and another unit operates only in the case of malfunction of the first unit. In xe2x80x98sharedxe2x80x99 mode of operation, each unit supplies a portion of the required power. These concepts are usually designated as xe2x80x98redundantxe2x80x99 or xe2x80x98parallelxe2x80x99 operation, and are also referred to as xe2x80x98N+1xe2x80x99 or xe2x80x98N+Xxe2x80x99 configuration.
As shown in FIG. 3, multiple power supply operation usually requires additional circuitry in the form of the supply adapters to control and manage the total operation. Each supply adapter is usually integrated into the corresponding power supply, making it capable of operation in an environment employing multiple power supplies. Various techniques for high performance methods for paralleling power supplies are described in U.S. Pat. No. 4,609,828.
FIG. 4 shows a common, simple, effective and cost-effective prior art network 50 for combining two DC power supplies 51 and 52 which provide power to a load 53 via respective supply adapters 54 and 55. The supply adapters 54 and 55 have respective positive outputs 56 and 56xe2x80x2 and negative outputs 57 and 57xe2x80x2. The negative outputs 57 and 57xe2x80x2 are commonly connected to the load 53 whilst the positive outputs 56 and 56xe2x80x2 are connected to the load 53 via respective rectifier diodes 58 and 59 whose anodes are connected to the respective positive outputs 56 and 56xe2x80x2. Such a mechanism allows for full redundancy: In the case of failure in either of the supplies, its associated diode will be reverse biased hence presenting high impedance, thus effectively disconnecting the power supply from the load. In addition, power supplies can be added and removed without disrupting the supply to the load. This technique is commonly referred to as xe2x80x98diode-summingxe2x80x99 or xe2x80x98ORxe2x80x99-ing diodes. The fact that the diode forward bias voltage Vƒ is directly proportional to the diode forward bias current Iƒ, leads to equal power distribution between the two power supplies 51 and 52 since they both provide half the total load current when both are operational. While this is not necessary in a redundant approach, it is preferable, as each power supply will see roughly the same power level.
Whilst multiple power supplies are known for sourcing a single load, there being no prior art provision to share multiple power supplies amongst a network which comprises more than one load, wherein the supplies are connected to distinct points in a network. In a network having a large number of loads, it is not feasible to multiple source all of the loads owing to both cost and space considerations. As a result, multiple sourcing is provided only in respect of high priority loads, whilst the remaining loads are commonly powered via the network bus. Moreover, since prior art networks provide for only a single power source to be connected to the network bus, a failure in that power source results in a total failure of the network and the length of conductors in the bus is inherently limited.
It is an object of the invention to provide a network whose communication media are based on conductors and which allows for the units connected to the communication media to be fed by multiple power sources.
According to the invention there is provided a network allowing for communication, sensing and control, said network comprising:
at least three nodes interconnected by a bus for conveying both power and data to said nodes, said bus including at least two power carrying conductors, and
at least two power supplies connected via respective source couplers across the power carrying conductors at different points thereof.
Preferably, there are connected to the nodes one or more payloads that may be powered by local power supplies so as to provide greater security and flexibility.
In such a network the wires constituting the network bus are unlimited in length, since additional power supplies can be added in order to compensate for resistive losses in the bus. Furthermore, redundancy is achieved against both power supply faults and network faults. Moreover, by allowing the live removal or insertion of power supplies to and from the network power bus, a xe2x80x9chot-pluggablexe2x80x9d redundant power supply system provides a practical way to achieve zero downtime required in some applications.